In the application fields of superconductors, much research has been conducted all over the world for practical use of high-temperature superconductors. There are a first-generation high-temperature superconducting tape and a second-generation high-temperature superconducting tape. The first-generation high-temperature superconducting tape can be fabricated through a powder in tube (PIT) process in which precursor powder is treated in a silver (Ag) pipe. The second-generation high-temperature superconducting tape is technically called as a coated conductor (CC). Institutes and companies of many countries have conducted research on CCs. Many fabricating methods have been developed for CCs. CCs have a more complicated multilayer structure than that of the first-generation high-temperature superconducting tape.
It is considered that a superconducting tape will become the first practical superconductor product since the discovery of a high-temperature superconductor in 1986. A high-temperature superconducting tape can carry about one hundred times greater current per unit area substantially with no loss as compared with a copper wire. Since heat generates in proportional to the power loss of an electric power device, the electric power device can be heated to a high temperature due to a power loss. Therefore, copper wires having a relatively large resistance are not suitable for high capacity power devices. However, high-temperature superconducting tapes can be usefully used for high capacity power devices. Niobium based low-temperature super conductors are not economical since they require expensive liquid helium due to their extremely low critical temperature. However, high-temperature superconducting tapes are economical since they require liquid nitrogen that can be easily obtained from air. Therefore, practical use of high-temperature superconducting tapes will mark a new era in large-scale energy industries. When the high-temperature superconductor was first discovered, although the high-temperature superconductor was considered to be the next generation of conductors, it was difficult to develop high-temperature superconducting tapes. However, recent dramatic technical development makes it possible to practically use of the high-temperature superconductor. For this, it is important to develop a method of rapidly fabricating superconducting tapes with low costs. There are many methods that can be practically used for fabricating superconducting tapes, such as a metal-organic deposition (MOD) method, a metal-organic chemical vapor deposition (MOCVD) method, and an evaporation using drum in dual chamber (EDDC) method. The EDDC method is disclosed in U.S. Pat. No. 6,147,033, filed by the applicant of the present invention, entitled “ Apparatus and method for forming a film on a tape substrate.”
In the EDDC method, a vacuum chamber divided into three chambers is used. In detail, a drum is rotated in an upper auxiliary chamber under oxygen gas atmosphere at a pressure of about 5 mTorr. A substrate tape having a width of about 4 mm and thickness of about 0.1 mm or less is wound around the drum. The substrate tape and the drum are heated to a temperature of about 700° C. and are rotated at a speed of about 1 revolution per second. A lower main chamber is kept at a pressure of about 0.01 mTorr. The low main chamber supplies raw materials such as samarium (Sm), barium (Ba), and copper (Cu) to the rotating substrate tape in the form of atomic vapor to form a high-temperature superconductor layer on the rotating substrate tape. Here, the ratio of the raw materials (for example, Sm:Ba:Cu=1:2:3) supplied from the main chamber is precisely maintained. While the substrate tape is being rotated between an evaporation region and a reaction region in the auxiliary chamber, the high-temperature superconductor layer is grown on the substrate tape.
However, since the length of the substrate tape wound around the drum is limited, a long high-temperature superconducting tape cannot be fabricated through the EDDC method. Therefore, it is necessary to improve the EDDC method to fabricate a sufficiently long high-temperature superconducting tape. For example, a high-temperature superconducting tape having a sufficiently large length can be fabricated using two reels coaxially disposed at both sides of a drum by depositing a superconductor material on the high-temperature superconducting tape while releasing the high-temperature superconducting tape from one real and winding the superconducting tape around the other reel. Here, the high-temperature superconducting tape is wound around inner regions of the reels.